chapter 18: waiting line analysis Flashcards

1
Q

when do waiting lines occur?

A

when there is a temporary imbalance between supply (capacity) and demand

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2
Q

downsides of waiting lines

A

add to the cost of operation

they reflect negatively on customer service

loss of goodwill

loss of business due to customers refusing to wait and going elsewhere

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3
Q

queueing theory

A

a mathematical approach to the analysis of waiting lines

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4
Q

Why Is There Waiting?

A

arrival times and service durations exhibit a high degree of variability

the system at times becomes temporarily overloaded, giving rise to waiting lines; at other times, the system is idle because there are no customers

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5
Q

The goal of queueing analysis

A

to minimize total costs

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6
Q

The two types of costs in a queueing situation

A

“cost” of customers waiting for service

cost of provision of capacity

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7
Q

ways management can reduce their customers’ perception of the waiting time

A
  • Determine the acceptable wait time for the operation
  • Try to keep the waiting time experienced by a customer consistent over time
  • Install distractions that entertain and involve customers
  • Inform the customer of the cause of an abnormal wait and peak times
  • Keep the line moving continuously
  • Use first come, first served discipline (fairness is important)
  • Allow customers to serve themselves
  • Prepare the customers for service before the actual service
  • Make people conscious of time only if they overestimate the wait time.
  • Keep staff who are not serving customers out of sight.
  • Try to segment customers by personality
  • Never underestimate the power of a friendly and attentive server
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8
Q

ways in which management can reduce waiting times by fixing the system constraints

A

Use temporary workers

Shift demand

Standardize the service

Look for a bottleneck

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9
Q

Model choice is dependent on which characteristics of the waiting line system under investigation

A
  1. Potential number of customers.
  2. Number of servers and structure of queueing system.
  3. Arrival and service patterns.

4 . Queue discipline (i.e., order of service).

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10
Q

an infinite source of customers situation

A

the potential number of customers greatly exceeds system capacity

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11
Q

a finite source of customers situation

A

When the potential number of customers is limited

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12
Q

Each server in the queueing system can handle how many customers at a time?

A

can handle one customer at a time

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13
Q

queueing system can have how many servers?

A

single or multiple serνers

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14
Q

true or false

Another distinctive of the queueing system characteristic is the number of steps or phases in a queueing system

A

true

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15
Q

advantage of a joint line of people waiting leading to multiple servers

A

first come first serve (fairness)

wait time will be less

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16
Q

disadvantage of a joint line of people waiting leading to multiple servers

which type of customers would prefer it

A

it might appear too long

may take a large space

servers may not work as fast as if they were responsible
for their own line

customers cannot choose their favorite server

homogeneous customers would prefer it

17
Q

advantages of separate lines leading to servers

which type of customer would prefer this

A

reduces the total variability of service durations, resulting in a reduced average wait time for all customers

heterogenous customers

18
Q

The most commonly used queueing models assume that the customer arrival rate can be described by which distribution?

A

The Poisson distribution

19
Q

The Poisson distribution

A

a one-parameter discrete probability distribution of the number of events occurring in an interval of time

–> provided that these events occur with a known average rate and independently of the time since the last event

20
Q

The exponential distribution

A

a one-parameter continuous probability distribution of the times between events that happen continuously and independently at a constant average rate

21
Q

reneging

A

customers grow impatient and leave the line

22
Q

jockeying

A

customers switch to another line

23
Q

balking

A

customers decide the line is too long and, therefore, do not enter the line

24
Q

Queue discipline

A

the order in which customers are served

25
Q

Operations managers typically look at which four measures when evaluating existing or proposed queueing systems

A
  1. The average number of customers waiting, either in line (not counting those being served) or in the system (including those being served)
  2. The average length of time customers wait, either in line or in the system
  3. Server utilization
  4. The probability that an arriving customer will have to wait for service or will have to wait more than a specified length of time before being served
26
Q

Server utilization

A

the proportion of time a server will be busy

reflects the extent to which the servers are busy rather than idle

27
Q

why would operations manager not necessarily want 100% server utilization?

A

increases in server utilization are achieved at the expense of greater increases in the average customer wait time

average customer wait time becomes exceedingly large as server utilization approaches 100 percent

100 percent utilization of servers leads to burnout

28
Q

which server utilization proportion is the most adequate?

A

between 80% and 90%

29
Q

the simplest queuing model

why?

A

model 1: Single Server, Exponential Service Durations

a system that has one server (or a single crew)

the queue discipline is First Come First Serve

customer arrival rates can be approximated by a Poisson distribution

service durations by an exponential distribution

30
Q

Model 3: Single Server, Constant Service Durations

A

a queueing system with constant service durations (and Poisson arrival rates)

–> to cut the average number of customers waiting in line in half (relative to Model 1)

31
Q

Model 5: Multiple Servers, Exponential Service Durations

A

poisson arrival rates with average tent symbol and exponential service durations with average 1/u

all M servers work at the same rate

customers form a single waiting line

the multiple server formulas are more complex than the single server formulas for Lq and Po.

32
Q

when does a multiple server system exist?

A

whenever there are two or more servers working individually to provide service to customers

33
Q

customer waiting cost

A

costs incurred by the organization due to customer waiting

34
Q

The optimal capacity (usually in terms of number of channels)

A

one that minimizes the sum of customer waiting costs and capacity or server costs

Minimize total cost = Total average customer wait cost + Total server pay cost

35
Q

what is used to identify the capacity size that will minimize total costs?

A

An iterative process

36
Q

Because the total cost curve is U-shaped, what does it mean for the total cost

A

the total cost will initially decrease as capacity is increased, and then it will eventually begin to increase

Once it begins to increase, additional increases in capacity will cause it to continue to increase